An aneurysm is a dilation of a blood vessel of at least 1.5 times above its normal diameter. A dilated vessel forms a bulge known as an aneurysmal sac that can weaken vessel walls and eventually rupture. Aneurysms are most common in the arteries at the base of the brain (i.e., the Circle of Willis) and in the largest artery in the human body, the aorta. The abdominal aorta, spanning from the diaphragm to the aortoiliac bifurcation, is the most common site for aortic aneurysms. Such abdominal aortic aneurysms (AAAs) typically occur between the renal and iliac arteries, and are presently one of the leading causes of death in the United States.
The two primary treatments for AAAs are open surgical repair and endovascular aneurysm repair (EVAR). Surgical repair typically includes opening the dilated portion of the aorta, inserting a synthetic tube, and closing the aneurysmal sac around the tube. Such AAA surgical repairs are highly invasive, and are therefore associated with significant levels of morbidity and operative mortality. In addition, surgical repair is not a viable option for many patients due to their physical conditions.
Minimally invasive endovascular aneurysm repair (EVAR) treatments that implant stent grafts across aneurysmal regions of the aorta have been developed as an alternative or improvement to open surgery. EVAR typically includes inserting a delivery catheter into the femoral artery, guiding the catheter to the site of the aneurysm via X-ray visualization, and delivering a synthetic stent graft to the AAA via the catheter. The stent graft reinforces the weakened section of the aorta to prevent rupture of the aneurysm, and directs the flow of blood through the stent graft away from the aneurismal region. Accordingly, the stent graft causes blood flow to bypass the aneurysm and allows the aneurysm to shrink over time.
Conventional stent grafts are made from surgical grade materials that are inherently thick and rigid, and therefore associated delivery systems typically have a size of approximately 20 Fr (i.e., approximately 6.7 mm in diameter) and greater. This size can be intrusive when placed through small iliac vessels, and accordingly cut-down procedures are used to introduce the delivery catheter. Cut-down procedures result in longer and more uncomfortable healing processes than if the stent graft was implanted using a smaller, percutaneously deliverable system. However, reducing the diameter of the delivery catheter (e.g., to allow for percutaneous implantation) increases the force required to unsheathe and expose the stent graft. This increased force also reduces control and precision during deployment, making it more difficult for a physician to implant the stent graft and potentially causing damage to the stent graft and/or the surrounding vessel walls.